A turbo charger that uses exhaust gas of an engine to increase intake gas of the engine includes a turbine impeller rotated by the exhaust gas and a compressor impeller that feeds air into a combustion chamber of the engine. The turbine impeller and the compressor impeller are fastened to each other via a shaft to form an assembly, and rotate in the turbo charger at high speed. Because the RPM of the assembly reaches 100,000 to 200,000 per minute, the center-of-mass of the assembly is displaced from the rotary axis, rotational balance degrades, contributing to noise and runout during high-speed rotation.
With a recent increase in demand for quietness of automobiles, the standard of rotational balance in the assembly (hereinafter referred to as impeller rotator) has gradually become strict. To correct imbalance of the impeller rotator, Japanese Unexamined Patent Publication No. 2008-223569 (Patent Document 1) describes that rotational balance is corrected by removing some parts from the turbo charger to form a gap behind the turbo charger, inserting a cutting tool into the gap, and cutting the back face of the turbine impeller with the tool.
This intends to correct overall rotational balance of the impeller rotator including the compressor impeller and the turbine impeller.